The present invention relates to microwave resonators and filters. More specifically, the invention relates to single multi-mode dielectric or cavity resonators.
A microwave resonator is a device that resonates an electromagnetic field. The size and shape of the resonator specify a particular frequency at which the resonator resonates electrical and magnetic signals. This resonance at the particular frequency is achieved by the periodic exchange of energy between the electric and magnetic fields that support the electric and magnetic signals that pass through the resonator. The lowest frequency that resonates within the rsonator is the fundamental mode of the resonator and is generally the frequency of interest in a resonator application. Higher order modes, or spurious modes, may interfere with the fundamental mode. Thus, it is desirable to filter such modes from the electromagnetic signals by filtering the signals outside the fundamental mode frequency.
Single resonators are used most often for frequency meters and frequency standards. A plurality of single resonators can be cascaded to form a microwave filter. An individual resonator in a cascading filter design is electro-magnetically coupled to another resonator through a small aperture or a wire. Generally, the resultant filter is a band pass filter that passes the pass-band frequencies. Resonators can be built where the shape of the resonator supports multiple modes. Adjacent resonators may be linearly coupled to form a filter, or alternatively, non-adjacent resonators may be coupled to form quasi-elliptical filters.
A dielectric single-mode resonator 2 from the prior art is shown in FIG. 1. In this known structure, a cylindrical disc 4 is mounted on a support 6 in a housing 8. Inside the disc 4, a magnetic field and an electric field is excited. The resonator 2 stores electric and magnetic energy within the housing 8. Resonance is achieved by the periodic exchange of energy between the electric and magnetic fields. This resonator configuration, however, supports only one particular field pattern 10 in the disc 4 at a particular resonant frequency. In addition, this structure is also relatively large.
FIGS. 2A-2D are views of a dielectric dual-mode resonator also known in the prior art. As shown in FIG. 2, a simiiar structure acting as a dual-mode resonator 12 may support two different electric and magnetic field patterns 14 and 16. The two modes are orthogonal, and thus do not exchange energy between the modes. The two modes may be coupled to each other by including a small disturbance to break the symmetry of the fields. Such a disturbance may be created by a tuning screw 18. This type of resonator may increase the spurious rejection of unwanted frequencies, but is still large.
FIGS. 3A-3C are views of a dielectric single-mode resonator using an electric wall, and is also known in the prior art. This single-mode dielectric resonator 22 resonates a frequency within a half disc 24. The dielectric half disc 24 is mounted on an electric conducting wall 26. The electric conducting wall electromagnetically images another half of the resonator just as an optical mirror images an optical figure. This resonator 22 reduces the resonator size to about half of the dielectric single-mode resonator of FIG. 1. There is, however, only one mode supported within the smaller dielectric filter 22, which has an electric field 28 perpendicular to the electric wall 26. The electric wall must be made of a lossy conductor and thus increases the energy loss within the resonator 22.
A dielectric resonator is provided having a cavity, a dielectric half disk resonator structure, and a support for the half disk resonator structure. The support isolates the dielectric half disk resonator structure from walls of the cavity. A straight edge wall of the dielectric half disk resonator structure couples to a dielectric/air interface within the cavity and forms an approximate magnetic wall. The approximate magnetic wall images the electric field perpendicular to the straight edge wall and supports a single-mode electric field within the half disk resonator structure. Multiple half disk resonator structures may be oriented within the cavity to support other, orthogonal electric fields. Multiple cavities may be coupled to each other through irises formed on the cavity walls.
One aspect of the invention provides a dielectric resonator comprising a cavity housing, a support mounted within the cavity housing, and a dielectric half disk resonator structure. The dielectric half disk resonator structure is mounted on the support and has a straight edge wall. The dielectric half disk resonator structure resonates an electric field perpendicular to the straight edge wall.
Another aspect of the invention provides a dielectric resonator comprising a cavity housing, a support mounted within the cavity housing, and first and second dielectric half disk resonator structures. The first dielectric half disk resonator structure is mounted on the support and has a first straight edge wall. The second dielectric half disk resonator structure has a second straight edge wall such that the second straight edge wall is isolated from the cavity housing. Each of the dielectric half disk resonator structures resonates an electric field.
Yet another aspect of the invention provides a dielectric resonator comprising a plurality of cavities, a cavity wall separating at least two of the cavities, and an iris formed on the cavity wall coupling the two cavities. Each of the cavities has a dielectric half disk resonator structure mounted such that a straight edge wall of the dielectric half disk resonator structure is isolated from the cavity wall.